|关键词: 青海湖 介形虫 丰度 氧碳同位素 季节和年际变化 控制因素
|Seasonal and interannual variations in abundance and oxygen carbon isotopic compositions of ostracod shells from Lake Qinghai and their controlling factors: A case study on the sediment trap
LI Yan1,2, JIN Zhang-dong1
1.State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment,
Chinese Academy of Sciences, Xi′an 710075, China; 2.University of Chinese Academy of Sciences, Beijing 100049, China
|Ostracoda are extremely sensitive to the aquatic environment and the substances of their shells are almost entirely from the water body where they live, thus chemical compositions of the shells have been used to reconstruct paleo-climate and environment. However, the current explanations about the controlling factors of different compositions of ostracod shells from Lake Qinghai are controversial and uncertainty. In this study, on the basis of the ostracod samples collected by a time-series sediment trap in Lake Qinghai from July 2010 to October 2011, seasonal and interannual variations in abundance and oxygen-carbon isotopic (δ18O, δ13C) compositions of two species of ostracod shells (Limnocythere inopinata and Eucypris mareotica) and their respective controlling factors were discussed, by correlating with the state-of-the-art sensing data of lake water by a CTD (Conductance, Temperature, Depth). The results show that the abundance of Limnocythere inopinata shells is an order of magnitude higher than that of Eucypris mareotica, but both ostracoda′ emergence and abundance variations are controlled directly by the lake water temperature. The δ18O and δ13C of both Limnocythere inopinata and Eucypris mareotica shells have distinctly interannual and seasonal variations, with species differences as well, whereas authigenic carbonates precipitated synchronously from water column have relatively uniform δ18O. Interannual differences of δ18O of two species of ostracod shells reflect directly the systematic differences of the summer water temperature between 2010 and 2011. Nevertheless, seasonal variations of δ18O of two species are not controlled by precipitation and evaporation (P/E) ratio, but by the precipitation of plenty of authigenic carbonates induced by high water temperature. The variations of δ13C of ostracod shells in Lake Qinghai are not controlled by any single factor, but might be related with lake temperature, authigenic carbonates precipitation and other factors. The control of authigenic carbonates precipitation on δ18O and δ13Cof Lake Qinghai ostracod shells proposed in this study would be an important implication for further understanding environmental significance of ostracoda and for withdrawing paleo-environmental information from chemical compositions of ostracod shells in past sediment in Lake Qinghai.
|Key words: Lake Qinghai ostracoda abundance oxygen and carbon isotopes seasonal and interannual variations controlling factors